USBTRANSFERMANAGEMENTFUNCTIONS

The USB standard defines four types of USB transfers. Control transfers,
Bulk transfers, Interrupt transfers and Isochronous transfers. All the
transfer types are managed using the following five functions:
usbd_transfer_setup() This function will allocate memory for and
initialise an array of USB transfers and all required DMA memory. This
function can sleep or block waiting for resources to become available.
udev is a pointer to "struct usb_device". ifaces is an array of
interface index numbers to use. See "if_index". pxfer is a pointer to an
array of USB transfer pointers that are initialized to NULL, and then
pointed to allocated USB transfers. setup_start is a pointer to an array
of USB config structures. n_setup is a number telling the USB system how
many USB transfers should be setup. priv_sc is the private softc
pointer, which will be used to initialize "xfer->priv_sc". priv_mtx is
the private mutex protecting the transfer structure and the softc. This
pointer is used to initialize "xfer->priv_mtx". This function returns
zero upon success. A non-zero return value indicates failure.
usbd_transfer_unsetup() This function will release the given USB
transfers and all allocated resources associated with these USB
transfers. pxfer is a pointer to an array of USB transfer pointers, that
may be NULL, that should be freed by the USB system. n_setup is a number
telling the USB system how many USB transfers should be unsetup. This
function can sleep waiting for USB transfers to complete. This function
is NULL safe with regard to the USB transfer structure pointer. It is
not allowed to call this function from the USB transfer callback.
usbd_transfer_start() This function will start the USB transfer pointed
to by xfer, if not already started. This function is always non-blocking
and must be called with the so-called private USB mutex locked. This
function is NULL safe with regard to the USB transfer structure pointer.
usbd_transfer_stop() This function will stop the USB transfer pointed to
by xfer, if not already stopped. This function is always non-blocking
and must be called with the so-called private USB mutex locked. This
function can return before the USB callback has been called. This
function is NULL safe with regard to the USB transfer structure pointer.
If the transfer was in progress, the callback will called with
"USB_ST_ERROR" and "error = USB_ERR_CANCELLED".
usbd_transfer_drain() This function will stop an USB transfer, if not
already stopped and wait for any additional USB hardware operations to
complete. Buffers that are loaded into DMA using
"usbd_xfer_set_frame_data()" can safely be freed after that this function
has returned. This function can block the caller and will not return
before the USB callback has been called. This function is NULL safe with
regard to the USB transfer structure pointer.

USBTRANSFERCALLBACK

The USB callback has three states. USB_ST_SETUP, USB_ST_TRANSFERRED and
USB_ST_ERROR. USB_ST_SETUP is the initial state. After the callback has
been called with this state it will always be called back at a later
stage in one of the other two states. The USB callback should not
restart the USB transfer in case the error cause is USB_ERR_CANCELLED.
The USB callback is protected from recursion. That means one can start
and stop whatever transfer from the callback of another transfer one
desires. Also the transfer that is currently called back. Recursion is
handled like this that when the callback that wants to recurse returns it
is called one more time.
usbd_transfer_submit() This function should only be called from within
the USB callback and is used to start the USB hardware. An USB transfer
can have multiple frames consisting of one or more USB packets making up
an I/O vector for all USB transfer types.
void
usb_default_callback(struct usb_xfer *xfer, usb_error_t error)
{
int actlen;
usbd_xfer_status(xfer, &actlen, NULL, NULL, NULL);
switch (USB_GET_STATE(xfer)) {
case USB_ST_SETUP:
/*
* Setup xfer frame lengths/count and data
*/
usbd_transfer_submit(xfer);
break;
case USB_ST_TRANSFERRED:
/*
* Read usb frame data, if any.
* "actlen" has the total length for all frames
* transfered.
*/
break;
default: /* Error */
/*
* Print error message and clear stall
* for example.
*/
break;
}
/*
* Here it is safe to do something without the private
* USB mutex locked.
*/
return;
}

USBCONTROLTRANSFERS

An USB control transfer has three parts. First the SETUP packet, then
DATA packet(s) and then a STATUS packet. The SETUP packet is always
pointed to by frame 0 and the length is set by usbd_xfer_frame_len() also
if there should not be sent any SETUP packet! If an USB control transfer
has no DATA stage, then the number of frames should be set to 1. Else
the default number of frames is 2.
Example1: SETUP + STATUS
usbd_xfer_set_frames(xfer, 1);
usbd_xfer_set_frame_len(xfer, 0, 8);
usbd_transfer_submit(xfer);
Example2: SETUP + DATA + STATUS
usbd_xfer_set_frames(xfer, 2);
usbd_xfer_set_frame_len(xfer, 0, 8);
usbd_xfer_set_frame_len(xfer, 1, 1);
usbd_transfer_submit(xfer);
Example3: SETUP + DATA + STATUS - split
1st callback:
usbd_xfer_set_frames(xfer, 1);
usbd_xfer_set_frame_len(xfer, 0, 8);
usbd_transfer_submit(xfer);
2nd callback:
/* IMPORTANT: frbuffers[0] must still point at the setup packet! */
usbd_xfer_set_frames(xfer, 2);
usbd_xfer_set_frame_len(xfer, 0, 0);
usbd_xfer_set_frame_len(xfer, 1, 1);
usbd_transfer_submit(xfer);
Example4: SETUP + STATUS - split
1st callback:
usbd_xfer_set_frames(xfer, 1);
usbd_xfer_set_frame_len(xfer, 0, 8);
usbd_xfer_set_flag(xfer, USB_MANUAL_STATUS);
usbd_transfer_submit(xfer);
2nd callback:
usbd_xfer_set_frames(xfer, 1);
usbd_xfer_set_frame_len(xfer, 0, 0);
usbd_xfer_clr_flag(xfer, USB_MANUAL_STATUS);
usbd_transfer_submit(xfer);

USBTRANSFERCONFIG

To simply the search for endpoints the usb module defines a USB config
structure where it is possible to specify the characteristics of the
wanted endpoint.
struct usb_config {
bufsize,
callback
direction,
endpoint,
frames,
index flags,
interval,
timeout,
type,
};
type field selects the USB pipe type. Valid values are: UE_INTERRUPT,
UE_CONTROL, UE_BULK, UE_ISOCHRONOUS. The special value UE_BULK_INTR will
select BULK and INTERRUPT pipes. This field is mandatory.
endpoint field selects the USB endpoint number. A value of 0xFF, "-1" or
"UE_ADDR_ANY" will select the first matching endpoint. This field is
mandatory.
direction field selects the USB endpoint direction. A value of
"UE_DIR_ANY" will select the first matching endpoint. Else valid values
are: "UE_DIR_IN" and "UE_DIR_OUT". "UE_DIR_IN" and "UE_DIR_OUT" can be
binary OR'ed by "UE_DIR_SID" which means that the direction will be
swapped in case of USB_MODE_DEVICE. Note that "UE_DIR_IN" refers to the
data transfer direction of the "IN" tokens and "UE_DIR_OUT" refers to the
data transfer direction of the "OUT" tokens. This field is mandatory.
interval field selects the interrupt interval. The value of this field
is given in milliseconds and is independent of device speed. Depending
on the endpoint type, this field has different meaning:
UE_INTERRUPT "0" use the default interrupt interval based on endpoint
descriptor. "Else" use the given value for polling rate.
UE_ISOCHRONOUS
"0" use default. "Else" the value is ignored.
UE_BULK
UE_CONTROL "0" no transfer pre-delay. "Else" a delay as given by this
field in milliseconds is inserted before the hardware is
started when "usbd_transfer_submit()" is called.
NOTE: The transfer timeout, if any, is started after that
the pre-delay has elapsed!
timeout field, if non-zero, will set the transfer timeout in
milliseconds. If the "timeout" field is zero and the transfer type is
ISOCHRONOUS a timeout of 250ms will be used.
frames field sets the maximum number of frames. If zero is specified it
will yield the following results:
UE_BULK xfer->nframes = 1;
UE_INTERRUPT xfer->nframes = 1;
UE_CONTROL xfer->nframes = 2;
UE_ISOCHRONOUS
Not allowed. Will cause an error.
ep_index field allows you to give a number, in case more endpoints match
the description, that selects which matching "ep_index" should be used.
if_index field allows you to select which of the interface numbers in the
"ifaces" array parameter passed to "usbd_transfer_setup" that should be
used when setting up the given USB transfer.
flags field has type "struct usb_xfer_flags" and allows one to set
initial flags an USB transfer. Valid flags are:
force_short_xfer
This flag forces the last transmitted USB packet to be
short. A short packet has a length of less than
"xfer->max_packet_size", which derives from
"wMaxPacketSize". This flag can be changed during
operation.
short_xfer_ok
This flag allows the received transfer length,
"xfer->actlen" to be less than "xfer->sumlen" upon
completion of a transfer. This flag can be changed during
operation.
short_frames_ok
This flag allows the reception of multiple short USB
frames. This flag only has effect for BULK and INTERRUPT
endpoints and if the number of frames received is greater
than 1. This flag can be changed during operation.
pipe_bof This flag causes a failing USB transfer to remain first in
the PIPE queue except in the case of "xfer->error" equal to
"USB_ERR_CANCELLED". No other USB transfers in the affected
PIPE queue will be started until either:
1 The failing USB transfer is stopped using
"usbd_transfer_stop()".
2 The failing USB transfer performs a
successful transfer.
The purpose of this flag is to avoid races when multiple
transfers are queued for execution on an USB endpoint, and
the first executing transfer fails leading to the need for
clearing of stall for example. In this case this flag is
used to prevent the following USB transfers from being
executed at the same time the clear-stall command is
executed on the USB control endpoint. This flag can be
changed during operation.
"BOF" is short for "Block On Failure"
NOTE: This flag should be set on all BULK and INTERRUPT USB
transfers which use an endpoint that can be shared between
userland and kernel.
proxy_buffer Setting this flag will cause that the total buffer size
will be rounded up to the nearest atomic hardware transfer
size. The maximum data length of any USB transfer is
always stored in the "xfer->max_data_length". For control
transfers the USB kernel will allocate additional space for
the 8-bytes of SETUP header. These 8-bytes are not counted
by the "xfer->max_data_length" variable. This flag can not
be changed during operation.
ext_buffer Setting this flag will cause that no data buffer will be
allocated. Instead the USB client must supply a data
buffer. This flag can not be changed during operation.
manual_status
Setting this flag prevents an USB STATUS stage to be
appended to the end of the USB control transfer. If no
control data is transferred this flag must be cleared.
Else an error will be returned to the USB callback. This
flag is mostly useful for the USB device side. This flag
can be changed during operation.
no_pipe_ok Setting this flag causes the USB_ERR_NO_PIPE error to be
ignored. This flag can not be changed during operation.
stall_pipe
Device Side Mode
Setting this flag will cause STALL pids to be
sent to the endpoint belonging to this
transfer before the transfer is started. The
transfer is started at the moment the host
issues a clear-stall command on the STALL'ed
endpoint. This flag can be changed during
operation.
Host Side Mode
Setting this flag will cause a clear-stall
control request to be executed on the
endpoint before the USB transfer is started.
If this flag is changed outside the USB callback function
you have to use the "usbd_xfer_set_stall()" and
"usbd_transfer_clear_stall()" functions! This flag is
automatically cleared after that the stall or clear stall
has been executed.
bufsize field sets the total buffer size in bytes. If this field is
zero, "wMaxPacketSize" will be used, multiplied by the "frames" field if
the transfer type is ISOCHRONOUS. This is useful for setting up
interrupt pipes. This field is mandatory.
NOTE: For control transfers "bufsize" includes the length of the request
structure.
callback pointer sets the USB callback. This field is mandatory.